A broadband development trend of wireless communication requires that performance such as a loss can remain basically unchanged when a radio frequency front-end duplexer of a base station has a smaller volume, a larger power capacity, and lower costs. A cavity filter is a traditional technology of the duplexer of the base station, where the technology is mature and costs are low. The cavity filter generally includes a cover and multiple cavity casings, and multiple resonance tubes are disposed in each cavity casing. A function of each cavity casing is equivalent to an electronic oscillation circuit. When the filter is tuned to a proper wavelength of a receive signal, the oscillation circuit may be represented as a parallel oscillation circuit that includes an inductance part and a capacitance part, and a resonance frequency of the filter may be adjusted by adjusting the inductance part or the capacitance part.
A capacitance adjustment method is adjusting spacing between the resonance tube and the cover, and adjustment of the spacing is generally implemented by rotating a tuning screw out of or into a screw hole on the cover. As a volume of a single cavity continuously decreases, surface current density of the single cavity increases and a loss continuously increases; a volume decrease also shortens a distance between conductor surfaces inside the single cavity, a decrease in an electric intensity threshold obtained when an air breakdown occurs is caused, and a power capacity becomes smaller. Therefore, a volume of the cavity filter is smaller, a loss is greater, and a power capacity filter is smaller, which cannot meet the requirement of a smaller volume and unchanged performance.
The cavity filter generally uses a metal resonator, that is, the cavity casing, the resonance tube, and the like are all made of metal materials, or metalized materials at least on inner surfaces of the cavity casing. In a case in which a TM (transverse magnetic) mode dielectric filter has a same volume as the single cavity of the cavity filter, because the TM mode dielectric filter uses a high-performance ceramic resonator to replace the metal resonator, a smaller insertion loss can be implemented when a conductor loss reduced by the high-performance ceramic resonator is greater than a dielectric loss brought by the high-performance ceramic resonator. In addition, because a position in which an electric field of the TM mode dielectric filter is the strongest is inside a dielectric, and breakdown electric intensity of a dielectric material is far higher than that of air, the power capacity can also be greatly improved. However, a high-performance ceramic material generally includes a rare earth, and a price of the rare earth is high because of a global scarcity of a rare earth resource.